1. Field of the Invention
The present invention relates to bacterial galactanase enzymes for use in different industrial applications, such as in the textile, detergent and cellulose fiber processing industries, and in particular to methods for modifying animal feed using such enzymes.
2. Description of the Related Art
Galactans and arabinogalactans are present in most plants as components of pectic hairy regions and can be found in high quantities e.g. in soy plant seed and in potatoes. Another good source for highly purified galactans and arabinogalactans is the water-soluble polysaccharide extracted with alkali from lupin fibre. This substrate can be treated with arabinofuranosidase (EC 3.2.1.55) resulting in a galactan with a very high content of galactose (more than 91%); such a substrate can be obtained from Megazyme, Australia.
Galactans and arabinogalactans are usually attached to O-4 of rhamnose residues in the rhamnogalacturonan backbone of the hairy region. The distribution and composition of the side chains vary considerably between different cell types and physiological states, but in general about half of the rhamnosyl units in the rhamnogalacturonan regions have side chains attached. The galactan side chains are in most plants type 1 galactans, which are composed of .beta.-1,4 linked galactopyranose with some branching points and a length of up to 60 saccharide units (DP60). Arabinofuranose residues or short arabinan oligomers can be attached to the galactan chain at the O -3 of the galactosyl unit, thus the name arabinogalactan. Galactans (or arabinogalactans) have an important function in the primary cell wall, where they interact with other structural components of the cell wall such as xyloglucans or arabinoxylans. Thus, they possibly serve to anchor the pectic matrix in the cell wall. Furthermore, they increase the hydration and water-binding capacity and decrease inter-chain association between pectin polymers, which is thought to be of importance for modulation of porosity and passive diffusion. (Carpita & Gibeaut, 1993, Plant J.,3, 1-30; O'Neill et al., 1990, Methods in Plant Biochemistry, 415-441; Selvendran, 1983, The Chemistry of Plant Cell Walls. Dietary Fibers; Hwang et al., Food Hydrocolloids, 7, 39-53; Fry, 1988, The Growing Plant Cell Wall: Chemical and Metabolic Analysis).
Beta-1,4-galactanases (EC 3.2.1.89) degrade galactans (and arabinogalactans) and have been purified from a variety of microbial sources (Nakano et al., 1985, Agric. Biol. Chem.,49, 3445-3454; Emi & Yamamoto, 1972, Agric. Biol. Chem., 36, 1945-1954; Araujo & Ward, 1990, J. Ind. Microbiol., 6, 171-178; Van De Vis et al., 1991, Carbohydr. Polym., 16, 167-187).
WO 92/13945 describes cloning and DNA sequencing of a fungal beta-1,4-galactanase from Aspergillus aculeatus.
WO 97/32014 describes cloning and DNA sequencing of fungal beta-1,4-galactanase from Humicola insolens and Myceliophthora thermophilum.
WO 97/32013 describes cloning and DNA sequencing of fungal beta-1,4-galactanase from Meripilus giganteus.
Braithwaite et al., BIOCHEMISTRY Vol. 36 , No. 49 pp. 15489-15500 (1997) disclose a galactanase from Pseudomonas fluorescens ssp. cellulose which is a retaining family 53 glycosyl hydrolase in which e161 and e270 are the catalytic residues.
WO 91/18521 describes a feed composition comprising, as a source of carbohydrates, a mannan-containing hemicellulose selected from soybeans, corn and alfalfa, as well as a mannanase that catalyzes the degradation of the mannan-containing hemicellulose.
Nakano et al., Eur. J. Biochem. 193(1): 61-67 (1990) describes the purification and characterization of an exo-1,4-.beta.-galactanase from a strain of Bacillus subtilis.
The database entries from the publicly available databases EMBL and Swissprot listed below refer to sequences with homology to the galactanases described herein:
Species Description wissprot/TREMBL EMBL Entry Bacillus Hypothetical 007013, 032260 Z94043, Z99121 subtilis protein Bacillus Hypothetical P48843 L03425 circulans protein
The galactanases in the list above and the galactanases of the invention belong to family 53 of glycosyl hydrolases (Henrissat B., A classification of glycosyl hydrolases based on amino-acid sequence similarities. Biochem. J. 280: 309-316 (1991)).
In spite of the state of the art e.g. as disclosed above, there remains a need for galactanase enzymes with improved activity for a number of different purposes. The object of the present invention is to provide galactanase enzymes with a high galactanase activity for use in industrial applications, such as the textile, detergent and cellulose fiber processing industries, and in particular for the modification of animal feed.